1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to an audio and/or video reproduction system, and more particularly, to an audio and video synchronization compensation method and apparatus for smoothly compensating synchronization of audio and video signals in an audio and video system, such as a DTV and a DVD player.
2. Description of the Related Art
Generally, a compressed signal reproduction system restores audio and video data from an MPEG2 transport stream or a program stream.
Since this compressed signal reproduction system uses a multiplexed digital signal, the system requires a separate audio and/or video (A/V) lip-synchronization apparatus or method to synchronize video and audio signals, unlike in existing analogue systems.
In addition to a video stream and an audio stream, a bitstream includes a system time clock (STC) corresponding to reference time information of a system and a presentation time stamp (PTS) indicating a time when restored data is to be reproduced, wherein the time is expressed with respect to the STC.
Accordingly, the compressed signal reproduction system checks the PTS with respect to the STC in each picture, and if the PTS exceeds a predetermined error range, the system adjusts the A/V lip-synchronization by using a skip or wait operation.
FIG. 1 is a graph explaining audio and video synchronization in a compressed signal reproduction system in the related art.
Referring to FIG. 1, an A/V synchronization interval 1 is a period of time in which audio and video signals are synchronized with an STC.
Reproduction intervals 2 and 3 are periods of time in which a video signal is displayed on a screen or an audio signal is output to a speaker according to a PTS.
Accordingly, if the PTC value of the current reproduction interval 2 and 3 is less than the STC value of the A/V synchronization interval 1, the compressed signal reproduction system skips a video or audio signal in units of frames (skip case). If the PTC value of the current reproduction interval 2 and 3 is greater than the STC value of the A/V synchronization interval 1, the compressed signal reproduction system waits for a video or audio signal in units of frames (wait case).
However, in the related art, if reception of radio waves is cut off due to an inferior environment or the system becomes unstable due to temperature changes, the difference between the STC time and the PTS time becomes large. As a result, if the difference between the STC time and the PTS time is too large, synchronization of audio and video signals takes more time, which may cause broken sound or broken screen phenomena.